Velocity redistribution of excited atoms by radiative excitation transfer. I. Experimental demonstration by photodissociation of Na₂ and field-free imaging

Radiation trapping which can imply dramatic changes in the apparent translation energy distribution of excited species after a unimolecular fragmentation process was demonstrated. It was noted that the radiative excitation transfer was on one hand similar to the dipole-dipole resonance excitation transfer discussed in the sense that the latter process can be seen as an exchange of virtual photons between the fast and the slow atoms. This paper emphasizes the importance of a proper account of radiation trapping phenomenon in any experiment involving atoms in resonance states, even in media-like supersonic beams, where one intuitively expects the effect of radiation trapping to be negligible.